A cassette seal comprises an inner and an outer ring having oppositely arranged L-shaped or angle profiles. When the inner and outer rings are placed together inside each other they form an essentially rectangularly bounded hollow space. The inner ring has on its inner surface a rubber coating to provide support and sealing with respect to an axle or shaft. The leg of one of the two rings which extends in the radial direction and which is positioned remotely from the sealed-off medium has mounted thereon an elastomer sealing lip which extends into the hollow space and rests resiliently against the leg of the other ring which extends in the axial direction. At least one dust lip is provided which is spaced from the sealing lip at an axial distance.
A cassette seal of the above-described type is known from European Patent Application 5707. The substantially rectangular hollow space which is enclosed by the inner and the outer ring can be freely acted upon by the pressure of the sealed-off medium. The sealing lip proper is arranged within the hollow space. Pressure shocks which may frequently occur [e.g., in the immediate vicinity of a wheel bearing] can lead to undesirable deformations and to damage of the sealing lip. Short duration pressure shocks can be particularly detrimental.
The sealing lip, which under opeating conditions is in frictional contact with the outer ring, is arranged in a U-shaped recess of the outer ring which opens toward the inside. Dirt that has penetrated into this space can form a firm crust under the action of centrifugal forces and can greatly impair the mobility of the sealing lip. This, likewise, can contribute to premature failure.